This invention relates to a channel-selecting apparatus for use in various multichannel receivers such as television (TV) or radio receiver, and more particularly to an improved channel-selecting apparatus of a mechanical contactless or electrically tuned type.
The prior art channel-selecting apparatus may be exemplified by a so-called mechanical contact type tuner adapted to select the oscillation frequencies of a local oscillator and/or the tuning frequencies of a radio-frequency (hereinafter referred to as RF) amplifier for all channels using a mechanical contact switch assembly of a rotary or push button type.
However, such mechanical contact type tuner has the drawback that the mechanical contacts are gradually worn away during long use, reducing their mutual connection.
For this reason, a so-called mechanical contactless or electrically tuned type tuner in which uses a frequency control element such as variable capacitance diode in place of the mechanical contact switch assembly has recently been more faborably accepted. The mechanical contactless type tuner is designed to determine the oscillation frequency of a local oscillator and/or the tuning frequency of an RF amplifier for each channel by electrically controlling voltages to be applied to the frequency control element.
However, the prior art electrically tuned type channel-selecting apparatus is generally adapted to previously adjust analogue dc voltages for all the channels being applied to such frequency control element by individual voltage control elements such as variable resistors and change the respective voltages in accordance with the channel selective operation.
Accordingly, the prior art electrically tuned type channel-selecting apparatus has the drawback that not only the requirement of a voltage control element such as a variable resistor for each channel presents difficulties in making the circuit of an entire channel-selecting apparatus suitable for integration, but also adjustment of the voltage control element consumes a relatively long time, resulting in the low yield and high cost of the apparatus.
It is, therefore, the object of this invention to provide a channel-selecting apparatus for multichannel receivers which eliminates the necessity of adjusting analogue dc voltage for each channel to be impressed on a frequency control element such as a variable capacitance diode for electrical control of the oscillation frequency of a local oscillator and/or the tuning frequency of an RF amplifier for each channel and in consequence has its electric circuit construction adapted for easy integration and moreover attains higher means production at low cost.